A rapid method for evaluating microbicidal activity of dentifrice formulations against salivary bacteria ex vivo

A new rapid ex vivo method was developed for evaluating the short-term bactericidal activity of dentifrices against salivary microorganisms. Dentifrice aliquots of 0.25 or 1.0 g were rapidly dispersed into 3.5 mL of freshly pooled human saliva, and 1.0 mL aliquots of the dentifrice-saliva suspension were collected after 30 or 60 seconds of exposure, diluted in neutralizing broth and plated on non-selective agar media for enumeration of surviving total cultivable microflora. Eight experimental dentifrices containing increasing amounts (0 to 2.6%) of a fixed ratio of essential oils (thymol, menthol, methyl salicylate and eucalyptol) were dispersed in saliva at a 0.25:3.5 (w/v) dentifrice:saliva ratio. Recoverable CFUs/mL at 30 sec. were reduced in a dose-responsive manner from > 10(6) to < 10(4). Additional tests using both 0.25 and 1.0 g amounts of dentifrice prototypes containing 2.1% of the essential oil mixture showed that the experimental dentifrices exhibited highly significant (approximately 2.5 log) reductions in viable recoverable microorganisms relative to essential oil-free placebos after both 30- and 60-second exposures. When compared to in vitro models previously used to evaluate the antimicrobial activity of dentifrices, this method provides a rapid, reproducible, more biologically representative means of screening dentifrice formulations for microbicidal activity using dilutions and exposure times approximating those achieved during toothbrushing. However, since other factors may influence microbicidal activity of dentifrice formulations in vivo, conclusions drawn using this model require clinical confirmation.